Northrop Grumman's B-2 Spirit bomber is mostly black or dark grey, but has a symmetric pattern of distinctive, thin white lines painted on its wings and fuselage. I have not been able to find anything similar on other airplanes, so why does the B-2 have these lines and what is their purpose?
@RAC and @Hobbes are right. I found a high res photo on defense.gov.
The crop below shows WALKWAY and NO STEP instructions indeed. Similar to what you'd find on a jetliner's wing.
It makes me wonder though why the person below did not abide.
Military aircraft, believe it or not, have relatively thin sheets of aluminum, titanium, composite, or honeycomb panels for much of the airframe. To prevent these more fragile areas from being damaged, the wing is marked with where it is and isn't safe to walk. As for the white footwear, these are typically just the equivalent of the disposable headgear you see doctors wear when they go into surgery on any doctor show on TV. They're to protect the paint, to prevent scuffs, and to prevent damaging any special paint coatings such as radar absorption (stealth).